Normally, a network of intelligent electronic devices (IEDs) will introduce a delay while messages are communicated through the network. Devices and protocols conventionally attempt to compensate for this delay by (a) making the network “fast” (i.e., reducing the communications delay to an insignificant proportion of the overall error), or (b) modeling the network to determine what the delay is and incorporating the estimated delay in the absolute time. Each of these conventional methods has drawbacks. The first method is not always possible, particularly for wide area networks spanning a large geographic area. The first method can also be expensive because a faster, high bandwidth, low latency network is needed to maintain accurate time-synching, but such a network may be entirely too advanced for an implementation where a low speed, low bandwidth, high latency network would otherwise be entirely sufficient. In the second method, a more accurate time synchronization message can be obtained versus the first method, but any variability in the communication latency of the network will increase the time error of the message. Because the communication latency variability in IED networks can be and commonly is larger than the acceptable error, the second method may not meet the accuracy requirements.
Clocks are known to shift over time and even though they may be synchronized at one point in time, eventually they fall out of synch and need to be resynchronized. In utility systems, it is known to synchronize the clocks of IEDs by sending data indicative of an absolute time reference, but this data is susceptible to the same communication delays and latencies in the network, so by the time the new time reference is received, the attendant delay in network communications and processing creates a slight offset between the device's clock and the master clock. Synchronization among IEDs in a utility system is important at least for critical event reporting and alarming. When multiple events occur very close in time to one another, it is important to determine which event was critical. Out-of-synch clocks exacerbate the ability to report accurately sequence-of-events and to diagnose problems associated therewith.
What is needed, therefore, is a more accurate method of synchronizing IEDs in a utility system, one that is immune from network or processing delays and latencies. Aspects of the present disclosure are directed to addressing this and other needs.